As technology relating to diode wave detection and rectenna, technologies disclosed in Japanese Patent No.2561023 (Document 1), Japanese Patent No. 2605827 (Document 2), JP-A-4-291167 (Document 3), JP-A-9-162644 (Document 4), Japanese Patent No. 2533800 (Document 5), and JP-B-6-48895 (Document 6) are known. Of these, Documents 1 through 4 disclose technology relating to high frequency wave detection using a diode, and Documents 5 and 6 disclose technology relating to rectenna.
First, high frequency wave detection technology using an ordinary diode disclosed in Documents 1 through 3 will be described. FIG. 11A shows a known diode detection circuit for performing high frequency wave detection. In the diode detection circuit shown in FIG. 11A, a bias voltage source B is connected to the anode side of a diode D via an inductance L0, and a resistance R01 and a capacitance C2 connected to ground are connected in parallel with each other to the cathode side of the diode D. However, the diode detection circuit shown in FIG. 11A is sometimes operated without a bias voltage being applied.
For example, when a low-level high frequency power is to be detected, generally, down to about −40 dBm a zero bias Schottky diode or the like can be used. When the high frequency power is of a lower level than that, normally, a slight bias voltage is applied. However, even when a bias voltage is applied, as will be further discussed later about −50 dBm constitutes a lower limit of high frequency wave detection.
To convert high frequency power into direct current, half-wave rectification is used; but when the circuit shown in FIG. 11A is used for that purpose, to convert a low-level high frequency power into a direct current it is necessary for the d.c. bias current to be made very small. For example to realize a bias current of 1 μA with a voltage of 3V, a resistance of 3 MΩ is necessary. In this case, the inductance L0 on the anode side of the diode D of FIG. 11A can be replaced with a resistance R02 (FIG. 11B)
However, in the cases of both FIGS. 11A and 11B, the resistances R01 and R02 used must be of several MΩ. When a resistance having a large resistance value like this is realized on an IC chip, the resistance element becomes long, and a large space becomes necessary. As a result, the facing area of the resistance element facing ground becomes large, a parasitic capacitance and a parasitic resistance arise between the resistance on the chip and the ground in the substrate, and the high frequency power leaks to the substrate. Consequently, to convert a low-level high frequency power of for example 5.8 GHz, −60 dBm into a direct current with a diode circuit formed on an IC chip is difficult.
Although it is possible to convert a low-level high frequency wave of −60 dBm into a direct current by using heterodyne detection technology, a transmitter or LAN and mixer must be operated continually, and the power consumed during high frequency signal standby time becomes large.
Also, with a high frequency detection circuit using a diode, it is notable that when the load resistance is large, the voltage applied across the anode/cathode of the diode becomes small and the high frequency wave cannot be converted, and that post-conversion output resulting from bias fluctuation is not distinguishable from d.c. potential obtained by converting high frequency power.
In Document 4, technology for producing a d.c. potential corresponding to an inputted high frequency power level is disclosed. That is, in Document 4, technology for converting a high frequency power of essentially any frequency into a d.c. current is disclosed. The technology of Documents 5 and 6 relates to rectenna, and discloses the use of received microwaves as a power source.
The present invention relates to a start signal outputting circuit capable of receiving a high frequency wave, generating a d.c. potential from that high frequency wave, and using this d.c. potential as a starting signal of a designated circuit, and particularly it is an object of the invention to provide a start signal outputting circuit having a construction suitable for integration. It is another object of the invention to provide a start signal outputting circuit capable of generating a low-noise d.c. potential when converting a high frequency signal into a d.c. potential.